The invention relates to a method for controlling an electric pad wear readjustment device of a disk brake arrangement, in particular for a motor vehicle. The invention also relates to a corresponding disk brake arrangement and to a disk brake.
Pad wear readjustment devices of said type are known in a variety of embodiments, such as for example mechanical readjusters with automatic adjustment of a friction point. In this case, the readjustment device is activated during every brake actuation, for example by way of a feed element of a brake-application device of the disk brake. In the event of wear of brake pads and brake disk, automatic readjustment of the pads is performed by means of the readjustment device, for example by way of an adjustment movement of pressure plungers of variable length.
European Patent Document No. EP 1 476 673 B1 describes a disk brake with a readjustment device driven by electric motor, and a method for controlling a disk brake.
Said arrangements have been proven in practice. However, microscopic mechanical movements and/or vibrations can impair a readjustment, that is to say a readjustment is for example performed incompletely, wherein an air clearance is too large, thus necessitating corresponding excess energy for braking processes. Possibilities for intervention for the purpose of preventing such impairment are not known.
It is the object of the present invention to provide an improved method for controlling a pad wear readjustment device for a disk brake arrangement.
It is a further object to provide an improved disk brake arrangement.
The electric pad wear readjustment device is controlled by energization of a clutch device of the electric pad wear readjustment device during a movement of the brake feed lever. The transmission of the torque produced by said brake feed lever to a readjustment spindle can be controlled by means of the switchable clutch device in a simple manner by way of a switch, for example a relay and/or a semiconductor switch.
A method according to the invention for controlling an electric pad wear readjustment device of a disk brake arrangement, in particular for a motor vehicle, with a disk brake and a control device, wherein the disk brake has a brake-application device with a brake feed lever, wherein the pad wear readjustment device is coupled to the brake feed lever and is preferably inserted into a readjustment spindle of the disk brake, comprises the following method steps: (S1) detecting an air clearance of the disk brake; (S2) identifying a change in the air clearance by comparison with preset values; and (S3) controlling the electric pad wear readjustment device by energizing an electromagnetic coil.
A disk brake arrangement according to the invention for carrying out the method according to one of the preceding claims has a disk brake, in particular for a motor vehicle, with a brake-application device with a brake feed lever, an electric pad wear readjustment device which is preferably insertable into a readjustment spindle of the disk brake, and a control device, wherein the electric pad wear readjustment device is coupled to the brake feed lever. The electric pad wear readjustment device comprises a readjustment shaft with an outer bearing; a rotary drive element; and a clutch device for the switchable coupling of the rotary drive element to the readjustment shaft. The clutch device is of electrically switchable form with at least one electromagnetic coil.
The brake feed lever can move without torque being transmitted in the electric pad wear readjustment device to the readjustment spindle. Only when the clutch device is activated is torque transmitted to the readjustment spindle.
Further advantageous refinements are specified in the subclaims.
In one embodiment, during the detection of the air clearance of the disk brake, a lever feed travel of the brake feed lever is detected. In this way, it is possible to identify whether the brake feed lever is situated in a range in which the air clearance is being passed through.
In a further embodiment, during the detection of the air clearance of the disk brake, a friction point is determined on the basis of the transmission of force by a readjustment spindle of the electric pad wear readjustment device, by virtue of the lever feed travel of the brake feed lever and an adjustment movement of the pad wear readjustment device in the event of energization of the electromagnetic coil being detected. If, during a feed movement of the brake feed lever, an adjustment movement takes place at the same time but then stops despite a further feed movement, the friction point has been reached. This may also be the case if no adjustment movement takes place at the start of a feed movement.
According to a yet further embodiment, it is possible for the energization of the electromagnetic coil to take place in a manner dependent on a detected movement of the brake feed lever. This is possible if a combination of pad wear sensor and feed lever sensor is provided in the pad wear readjustment device.
In another embodiment, during the detection of the air clearance of the disk brake, a pressure measurement may be performed at a preset braking point in comparison with a preset setpoint characteristic curve. Additional monitoring of the friction point can be realized in this way. Furthermore, it is possible in this case for reliability of pressure regulation to be improved by way of rapid fault detection in the event of a faulty pressure sensor.
In this case, an identification of a friction point may be performed by the evaluation of a measured static brake pressure in a manner dependent on a movement of the brake feed lever. In this case, it may for example be provided that a setpoint characteristic curve is stored in table form in a memory device and can be taken into consideration for comparison purposes.
The control of the electric pad wear readjustment device by energization of the electromagnetic coil during a brake-application movement of the brake feed lever for the purpose of readjustment of the electric pad wear readjustment device is performed if a change in the air clearance in the sense of an increase of the air clearance has been identified.
It is however also possible for an excessively small air clearance to be reset to a presettable value again. For this purpose, in a further embodiment, it is provided that the control of the electric pad wear readjustment device by energization of the electromagnetic coil during a release movement of the brake feed lever for the purpose of retraction of the electric pad wear readjustment device is performed if a change in the air clearance in the sense of a reduction of the air clearance has been identified.
In a yet further embodiment, the control of the electric pad wear readjustment device by energization of the electromagnetic coil during the brake-application movement of the brake-application device may be performed shortly before a brake feed movement after the air clearance has been passed through, at the start of a brake feed movement after the air clearance has been passed through, upon the release of the brake-application device after the brake feed movement at the end of the release of the brake-application device, or outside the brake feed movement. In this way, an adjustment of the brake pad(s) may be performed as a feed movement, owing to wear, and also as a retraction movement. Thus, the air clearance between brake pad and brake disk can be adjusted. A retraction movement is possible if the clutch device is activated during a backward movement of the brake feed lever.
A further embodiment provides that the energization of the electromagnetic coil is performed by way of at least one short switching pulse. It is also possible for said energization to be performed by way of multiple switching pulses which are for example variable. Thus, the energization of the electromagnetic coil may be performed for example by way of PWM (pulse width modulation).
The electromagnetic coil may also be energized by way of PWM or other suitable actuation regimes such that, for example, an adjustable overload clutch can thereby be formed.
In a further embodiment, it is provided that the disk brake arrangement has the electric pad wear readjustment device with at least one pad wear sensor which may for example be in the form of an angle sensor. The pad wear sensor may also may be the subject of an independent application. It is thus possible for a readjustment process to be performed in targeted fashion in a manner dependent on the wear of brake pads and brake disks by virtue of the clutch device being correspondingly activated and deactivated.
In another embodiment, the at least one pad wear sensor is at least partially a constituent part of the connection device. A particularly compact and simple construction is thus possible.
In another embodiment of the disk brake arrangement, the electric pad wear readjustment device has at least one feed lever sensor, which may also be the subject of an independent application. This, too, may at least partially be a constituent part of a connection device, and may for example also be in the form of an angle sensor. Here, as is likewise provided in the case of the pad wear sensor, a feed sensor element may be arranged in the connection device and interact with a feed encoder element which is coupled to the brake feed lever.
In one embodiment, the control device may be arranged on the electric pad wear readjustment device and thus form a so-called standalone version. In this way, retrofitting of existing series-produced disk brakes is possible because, for example, previous electromechanical potentiometers can be electronically reproduced, wherein terminals for potentiometers provided on a control unit can continue to be used by the reproduced terminals, for example by the control device.
The pad wear readjustment device has a terminal device which is connected in electrically conductive fashion to the at least one electromagnetic coil. The electromagnetic coil is electrically connected by means of a plug connection. In this way, it is possible for the connection device to be easily and quickly changed in the event of maintenance or exchange work, without the need to break or produce special electrical connections by means of tools.
In an alternative embodiment of the disk brake arrangement, the control device may be a constituent part of a controller, for example of a pressure regulating module, and/or brake control unit. A broad area of use is thus realized.
By means of the electric pad wear readjustment device, the electromagnetic clutch can realize not only pad wear readjustment but also pad retraction, for example in the event of a fault or in the event of exchange of the brake pads and maintenance. Thus, air clearance regulation can also be made possible in a simple manner. In this case, the drive source is, as in previous mechanical readjustment devices, the brake feed lever.
The pad wear readjustment device has a terminal device which, in one version, outputs an analog signal of the pad wear sensor and of the feed lever sensor (if used). For this purpose, the terminal device has a control device, for example a microcomputer. The terminal device may however also transmit the sensor signals digitally, without a control device, to a superordinate control unit with corresponding control device.
In the event of a fault of the electric brake (for example absence of a 5 V supply voltage of a potentiometer) being identified, the follow-up movement of the brake pad can be ensured. This is realized by actuation of the electromagnetic coil after identification of the air clearance having been passed through, as long as the brake is still moving in the feed direction, but not during the release of the brake.
The standalone version is compatible with previous designs and is thus exchangeable for retrofitting purposes.
The pad wear readjustment device furthermore has the following advantages:                autarkic electric pad detection and readjustment        analog pad wear output        high possible torque for adjustment by means of toothed clutch        reliable holding force by means of one, preferably two friction surfaces (ramp-type toothings are also possible instead of friction surfaces)        simple robust construction        dedicated supply voltage        pad wear follow-up movement even during emergency operation of the brake (backup)        
The pad wear readjustment device may furthermore have an overload clutch, for example a ball ramp clutch or helical toothing.
A disk brake, in particular for a motor vehicle, having a brake-application device with a brake feed lever and at least one readjustment spindle, has the above-described at least one electric pad wear readjustment device of the above-described disk brake arrangement.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.